On the retardation mechanisms of citric acid in ettringite-based binders

Abstract This study aims to obtain insights into the retardation mechanism of citric acid in an ettringite-based binder from ladle slag and gypsum. The hydration kinetics and phase assemblage of the binder were experimentally investigated and thermodynamically modelled. Additionally, the effects of citric acid on synthetic ettringite were studied to obtain further understanding of the interaction between this organic ligand and the crystal. Experimental results reveal that citric acid works as an inhibitor of ettringite’s formation leading to the precipitation of monosulfate and gypsum; the ettringite surface blockage by citrate ligand effectively prevents precipitation of this crystal. This leads to an overestimation in the precipitation of ettringite in the thermodynamic model due to this kinetic barrier imposed by the ligand. Thermodynamic modelling suggests ettringite, monosulfate, aluminum hydroxide, and strätlingite as main hydrates in this binder, whereas an intermixed C–(A–)S–H gel was observed experimentally instead of strätlingite

Radiological and leaching assessment of an ettringite-based mortar from ladle slag and phosphogypsum

Abstract In this investigation, ettringite-based mortars were synthesized from ladle slag (LS) and phosphogypsum (PG), promoting the concept of a circular economy. However, the reuse of naturally occurring radioactive materials (NORM), such as PG, requires radiological investigation. Also, the immobilization degree for contaminants contained in PG should be evaluated. The former was investigated using gamma spectroscopy and radon exhalation/emanation tests, while the latter was assessed using an up-flow percolation column test according to the CEN/TS 16637‐3. The produced mortars comply with current legislation on naturally occurring radionuclides (NOR) in building materials, proving that they can be safely used for building purposes. The radon emanation decreased upon increasing the Polish PG content, which was mainly determined by the microporosity. The specific surface areas were 20‐30 times lower than conventional cement, and the immobilization degree for contaminants was generally high (>90%). This investigation demonstrates high potential for PG reuse in ettringite-based mortars

The sycamore maple bacterial culture collection from a TNT polluted site shows novel plant-growth promoting and explosives degrading bacteria

Military activities have worldwide introduced toxic explosives into the environment with considerable effects on soil and plant-associated microbiota. Fortunately, these microorganisms, and their collective metabolic activities, can be harnessed for site restoration via in situ phytoremediation. We characterized the bacterial communities inhabiting the bulk soil and rhizosphere of sycamore maple (Acer pseudoplatanus) in two chronically 2,4,6-trinitrotoluene (TNT) polluted soils. Three hundred strains were isolated, purified and characterized, a majority of which showed multiple plant growth promoting (PGP) traits. Several isolates showed high nitroreductase enzyme activity and concurrent TNT-transformation. A 12-member bacterial consortium, comprising selected TNT-detoxifying and rhizobacterial strains, significantly enhanced TNT removal from soil compared to non-inoculated plants, increased root and shoot weight, and the plants were less stressed than the un-inoculated plants as estimated by the responses of antioxidative enzymes. The sycamore maple tree (SYCAM) culture collection is a significant resource of plant-associated strains with multiple PGP and catalytic properties, available for further genetic and phenotypic discovery and use in field applications.This work was supported by a grant from FWO-Flanders, Belgium, and the Methusalem project 08M03VGRJ.Peer Reviewe